What is the Difference Between Capsid and Nucleocapsid

The main difference between capsid and nucleocapsid is that capsid is the protein shell of the virus whereas nucleocapsid is the capsid and the nucleic acid of the virus.

Capsid and nucleocapsid are two structures of the virus. Generally, a virus is an infective agent that typically consists of a nucleic acid molecule in a protein coat, is too small to be seen by light microscopy, and is able to multiply only within the living cells of a host. In addition, the genetic material can be either DNA or RNA in viruses.

Key Areas Covered

1. What is Capsid
   • Definition, Characteristics, Importance
2. What is Nucleocapsid
   • Definition, Characteristics, Importance
3. Similarities Between Capsid and Nucleocapsid
   • Outline of Common Features
4. Difference Between Capsid and Nucleocapsid
   • Comparison of Key Differences

Key Terms

Capsid, Nucleocapsid

What is Capsid

A capsid is a protective coat of protein in viruses that protects the genetic material. The proteins that make up the capsid are capsid proteins. The three-dimensional morphological subunits in the capsid are capsomers. Protomers are the oligomeric, repeating structural subunits of the capsid. In addition, capsids occur in three different shapes: icosahedral, helical, and prolate. Most viruses are icosahedral and helical in shape. But, some viruses such as bacteriophages have more complicated shapes. In the formation of the viral envelope, the capsid is coated with a lipid membrane.

Figure 1: Capsid

Furthermore, the main function of the viral capsid is to protect the inner contents of the virus. Generally, capsids protect the virus from extreme temperatures, pH differences, radiation, chemicals, and enzymes. During replication, the protein biosynthesis pathways of the host cell produce new viral capsid proteins.  

What is Nucleocapsid

The nucleocapsid is the capsid and the inner genome of a particular virus. Besides, the viral genome may contain DNA or RNA. Depending on their content, there are two types of viruses: DNA viruses and RNA viruses. However, many viruses have RNA genomes. Moreover, the genetic material of the virus can be either single-stranded or double-stranded. Further, the sense of the genetic material can be either positive or negative. On the other hand, the shape of the genetic material of the virus can be either linear, circular, or segmented. Therefore, depending on the above characteristics of the genome, viruses can be classified into groups.

Figure 2: Virus Structure

Moreover, the main function of the nucleocapsid is to protect the viral genome. During the replication of viruses, the host cell machinery replicates the viral genome.

Similarities Between Capsid and Nucleocapsid

• Capsid and nucleocapsid are two structures of a virus.
• A virus contains genetic material encased in a protein coat.
• Moreover, a virus undergoes replication inside the host cell using host cell machinery.

Difference Between Capsid and Nucleocapsid

Definition

Capsid refers to the protein shell of the virus while nucleocapsid refers to the capsid and the nucleic acid of the virus.

Significance

Generally, capsid contains capsid proteins while nucleocapsid contains viral genome.

Function

The main function of the viral capsid is to protect the inner contents of the virus while the main function of the nucleocapsid is to house the viral genome.

Conclusion

In brief, the capsid is the protein shell of the virus and is made up of capsid proteins. Further, its function is to protect the content of the capsid mainly the genetic material of the virus. In contrast, the nucleocapsid is the capsid and the nucleic acid. Therefore, the viral genome occurs inside the capsid. However, the main function of the nucleocapsid is to protect the viral genome. Hence, the main difference between capsid and nucleocapsid is their structure.

References:

1. Battista, J. (n.d.). Capsid: Definition, Function & Structure. Study.com | Take Online Courses. Earn College Credit. Research Schools, Degrees & Careers. Retrieved September 14, 2022.
2. Wikimedia Foundation. (2022, August 19). Virus. Wikipedia. Retrieved September 14, 2022.

Image Courtesy:

1. “Helical capsid with RNA” By Thomas Splettstoesser (www.scistyle.com) – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “HI-virion-structure en” By Thomas Splettstoesser – Own Work (Pixabay License) via Commons Wikimedia